Disazo compound having an anthraquinone nucleus

ABSTRACT

A disazo compound is provided which is represented by the formula (I): ##STR1## (wherein, R 1  and R 2  each stands for hydrogen, a lower alkyl group with 1-4 carbon atoms, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted hetero ring group. R 1  and R 2  may be the same or different. And, R 1  and R 2  may mutually bond to form a ring). 
     This disazo compound may be obtained by diazotating 2.6-diaminoanthraquinone and reacting the same with a coupler represented by the formula (IV): ##STR2## (wherein, R 1  and R 2  are the same as defined above). Further, a multilayer type electrophotographic element is provided which comprises a charge carrier generating layer and a charge transfer layer and uses, as a charge carrier generating substance, a disazo compound represented by the formula (I).

This is a division of application Ser. No. 536,924, filed Sept. 28,1983, now U.S. Pat. No. 4,537,844, issued Aug. 27, 1985.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a novel disazo compound, a method ofmaking same and an electrophotographic element, in particular amultilayer type electrophotographic element which comprises a chargecarrier generating layer containing a substance capable of generatingcharge carriers when exposed to radiation of light (which will be calleda charge carrier generating substance hereinafter) and a charge transferlayer containing a substance capable of accepting charge carriersgenerated from said charge carrier generating layer and transferringthem (which will be called a charge transfer layer hereinafter).

(2) Description of the Prior Art

As electrophotographic elements there have typically been used inorganicones using selenium and its alloys or dispersed coloringmatter-sensitized zinc oxides in a binder resin, and organic ones usingcharge transfer complexes of 2,4,7-trinitro-9-fluorenone (which will becalled TNF hereinafter) and poly-N-vinylcarbazole (which will be calledPVK hereinafter) and the like. However, the fact is that these elementshave a number of advantages as well as various disadvantages. Forinstance, the now widely used selenium element is defective in that themanufacturing conditions are complicated, the production cost isexpensive, it is difficult to form into a belt-like shape due to lack offlexibility, and attention must be paid in handling because it is verysensitive to heat and mechanical impact. The zinc oxide element isinexpensive because it can be prepared by coating the substrate with acheap zinc oxide, but defective in that it is generally inferior insensitivity and mechanical properties such as surface smoothness,tensile strength, friction resistance and the like. Therefore, the zincoxide element involves various problems such as durability and the likewhen used repeatedly in plain paper copying machines. And, the elementusing the charge transfer complex of TNF and PVK is too low insensitivity to be suitably used in high-speed copying machines.

In recent years, a wide range of studies has been carried out in orderto eliminate the shortcomings inherent in these elements. In particular,various organic elements have been proposed for that purpose. Amongthem, multilayer type elements are attracting public attention aselements for use in plain paper copying machines due to their highsensitivity and stable chargeability as compared with usual organicelements, said multilayer type element comprising an electricallyconductive substrate; a thin charge carrier generating layer formed onsaid substrate by depositing a charge carrier generating pigment capableof generating charge carriers on exposure to light in the proper way,for instance, such as vacuum vapor-deposition, coating a pigmentsolution or coating a dispersion of fine powdery pigment in a resinsolution; and a charge transfer layer, formed thereon, in which thecharge carriers generated by the charge carrier generating layer can beinjected with efficiency and transferred. And, some of them are put topractical use.

As the conventional multilayer type elements of this sort there areknown

(1) the multilayer type element using, as the charge carrier generatinglayer, a thin layer formed by vacuum-vapordepositing a perylenederivative and incorporating an oxadiazole derivative in the chargetransfer layer (which see U.S. Pat. No. 3,871,882),

(2) the multilayer type element using, as the charge carrier generatinglayer, a thin layer formed by coating an organic amine solution ofChloro Dian Blue and incorporating a hydrazone compound in the chargetransfer layer (which see Japanese Patent Publication No. 42380/1980),

(3) the multilayer type element using, as the charge carrier generatinglayer, a thin layer formed by coating an organic solvent dispersion ofdistyrylbenzene type disazo compound and incorporating a hydrazonecompound in the charge transfer layer (which see Japanese Laid OpenPatent Application No. 84943/1980), and the like.

However, the fact is that even in the multilayer type elements of thissort the conventional ones have a number of advantages as well asvarious disadvantages.

The element using the perylene and oxadiazole derivatives disclosed inthe preceding (1) involves the problems that the cost of production israised because the charge carrier generating layer is formed by vacuumvapordeposition, and the sensitivity is insufficient to be used in thehigher speed copying machines even if there is caused no problem whenused for practical purpose.

The element using the Chloro Dian Blue and hydrazone compound disclosedin the preceding (2) is superior in sensitivity but involves manydisadvantages in the preparation because there is necessity of using ahard-to-handle organic amine (for instance, ethylenediamine) as acoating solvent for the formation of the charge carrier generatinglayer. Further, this element is inferior in the reproductivity of redimages from the original because its sensitivity visible lightwavelengths covers the range of about 450 to 660 nm. This necessitatesemploying a filter to filter out red light when setting this elementactually in the copying machine, thereby exerting anunprofitable-influence upon the copying machine design.

The element using the distyrylbenzene type disazo compound and hydrazonecompound disclosed in the preceding (3) is very profitable in thepreparation because the charge carrier generating layer can be formedreadily by coating a dispersion of disazo compound, but is defective,like the element disclosed in the preceding (2), in that thereproductivity of red images from the original is inferior because itssensitive light wavelengths cover the range of about 450 to 700 nm.

As the disazo compounds used in the multilayer type elements there arealso known for instance the benzidine type disazo compound disclosed inJapanese Laid Open Patent Application Nos. 37543/1972 and 55643/1977,the stilbene type disazo compound disclosed in Japanese Laid Open PatentApplication No. 8832/1977 and the like.

However, the multilayer type elements using these conventional disazocompounds were generally inferior in sensitivity and deteriorated in thereproductivity of red images from the original because their sensitivelight wavelengths cover the range of about 450 to 700 nm. Accordingly,these elements exerted an unprofitable influence upon the copyingmachine design because the above disadvantages necessitate employing afilter to filter red light when setting these elements actually in thecopying machines.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel disazocompound used effectively in electrophotographic elements, in particularthe above mentioned multilayer type elements.

It is another object of the present invention to provide a method ofmaking said disazo compound.

It is a further object of the present invention to develop a multilayertype element which can be produced readily, is high in sensitivity andwhose sensible light wavelengths are localized in the short wavelengthrange, 450-600 nm, in other words, which is superior in thereproductivity of red images from the original.

The present invention relate to a novel disazo compound represented bythe general formula (I): ##STR3## (wherein, R₁ and R₂ each stands forhydrogen, a lower alkyl group with 1-4 carbon atoms, a substituted orunsubstituted aralkyl group, a substituted or unsubstituted aromaticgroup, or a substituted or unsubstituted hetero ring group, R₁ and R₂may be the same or different. And, R₁ and R₂ may mutually bond to form aring.)

In the general formula (I), the lower alkyl group includes an ethylgroup, a propyl group or the like; the aralkyl group includes a benzylgroup, a phenetyl group or the like; the aromatic group includes aphenyl group, a naphthyl group, an anthryl group, a pyrenyl group, ananthraquinonyl group or the like; and the hetero group includes athienyl group, a furyl group, a pyridyl group and a carbazolyl group.The ring formed cooperatively by R₁ and R₂ includes a hexylidene ring, apentylidene ring, a benzopentylidene ring and a dibenzopentylidene ring.And, as the substituents on the aralkyl group, the aromatic group, thehetero ring group or the ring formed by the cooperation of R₁ and R₂there can be enumerated a lower alkyl group with 1-4 carbon atoms, alower alkoxy group with 1-4 carbon atoms, halogen, a cyano group, anitro group, a lower dialkylamino group with 2-8 carbon atoms and thelike.

The disazo compound represented by the general formula (I) of thepresent invention, as mentioned above, is effective as the material foruse in the electrophotographic element, in particular is effective asthe charge carrier generating material for use in the multilayer typeelectrophotographic element. Further, the disazo compound according tothe present invention is useful as the charge carrier generatingsubstance in the electrophotographic element which has the monolayertype photosensitive layer formed by dispersing the charge carriergenerating substance and the charge transfer substance in the resin, andis also useful as the photoconductive substance in theelectrophotographic element which has the photosensitive layer formed bydispersing the photoconductive substance in the resin.

The present invention also relate to a process for manufacturing adisazo compound represented by the general formula (I): ##STR4##(wherein R₁ and R₂ are the same defined above), which comprises thesteps of diazotating 2,6-diaminoanthraquinone represented by the formula(II): ##STR5## into tetrazonium salt represented by the general formula(III): ##STR6## (wherein, Y stands for an anion functional group.), andthen reacting this tetrazonium salt with a coupler represented by thegeneral formula (IV): ##STR7## (wherein, R₁ and R₂ are the same definedabove).

In this manufacturing process, the diazotation of2,6-diaminoanthraquinone is carried out by adding sodium nitrite theretoat a temperature of -10° C. to 50° C. in an inorganic acid, forinstance, such as hydrochloric acid or sulfuric acid. This diazotationreaction completes in the time ranging from 30 minutes to 3 hours.

It is preferable that the resulting reaction mixture is further addedwith for instance borofluoric acid or an aqueous sodium borofluoricsolution to thereby cause precipitation of tetrazonium salt, and isemployed in the next reaction after the precipitated crystals arefiltrated therefrom. Then, this tetrazonium salt is reacted with thecoupler represented by the general formula (IV) to thereby cause acoupling reaction. Practically, this reaction is carried out bypreparing a mixed solution of tetrazonium salt, coupler and an organicsolvent such as N,N-dimethylformamide (DMF), dimethyl sulfoxide or thelike, and dropping an aqueous alkali solution, for instance, such as anaqueous sodium acetate solution therein at a temperature of about -10°C. to 40° C. This reaction completes in about 5 minutes to 3 hours.After completion of said reaction, separated crystals are filtrated andrefined by using a proper way (for instance, washing with water or/andorganic solvent, recrystallization or the like). Thus, the preparationof said disazo compound is completed.

The present invention is further directed toward a multilayer typeelectrophotographic element comprising forming, on an electricallyconductive substrate, a charge carrier generating layer and a chargetransfer layer, wherein said charge carrier generating layer containstherein a disazo compound represented by the general formula (I):##STR8## (wherein, R₁ and R₂ each stands for hydrogen, a lower alkylgroup with 1-4 carbon atoms, a substituted or unsubstituted aralkylgroup, a substituted or unsubstituted aromatic group, or a substitutedor unsubstituted hetero ring group. R₁ and R₂ may be the same ordifferent. And, R₁ and R₂ may mutually bond to form a ring.)

In the general formula (I), the lower alkyl group includes an ethylgroup, a propyl group or the like; the aralkyl group includes a benzylgroup; a phenetyl group or the like; the aromatic group includes aphenyl group, a naphthyl group, an anthryl group, a pyrenyl group, ananthraquinonyl group or the like; and the hetero group includes athienyl group, a furyl group, a pyridyl group and a carbazolyl group.The ring formed cooperatively by R₁ and R₂ includes a hexylidene ring, apentylidiene ring, a benzopentylidiene ring and a dibenzopentylidienering. And, as the substituents on the aralkyl group, the aromatic group,the hetero ring group or the ring formed by the cooperation of R₁ and R₂there can be enumerated a lower alkyl group with 1-4 carbon atoms, alower alkoxy group with 1-4 carbon atoms, halogen, a cyano group, anitro group, a lower dialkylamino group with 2-8 carbon atoms and thelike.

The multilayer type element according to the present invention should besaid to be a superior one for use in copying machines because it isproduced readily, high in sensitivity and further its sensitivewavelengths are localized at the short wavelength region (450 to 600nm).

Next, the concrete examples of the disazo compound according to thepresent invention will be shown in Table 1 through Table 3.

                                      TABLE 1                                     __________________________________________________________________________     ##STR9##                                                                     Compound                                                                      No.          R.sub.3  R.sub.4  R.sub.5   R.sub.6  R.sub.7                     __________________________________________________________________________    1-1          OCH.sub.3                                                                              H        H         H        H                           1-2          H        OCH.sub.3                                                                              H         H        H                           1-3          H        H        OCH.sub.3 H        H                           1-4          CH.sub.3 H        H         H        H                           1-5          H        CH.sub.3 H         H        H                           1-6          H        H        CH.sub.3  H        H                           1-7          F        H        H         H        H                           1-8          H        F        H         H        H                           1-9          H        H        F         H        H                           1-10         Cl       H        H         H        H                           1-11         H        Cl       H         H        H                           1-12         H        H        Cl        H        H                           1-13         Br       H        H         H        H                           1-14         H        Br       H         H        H                           1-15         H        H        Br        H        H                           1-16         CN       H        H         H        H                           1-17         H        H        CN        H        H                           1-18         NO.sub.2 H        H         H        H                           1-19         H        NO.sub.2 H         H        H                           1-20         H        H        NO.sub.2  H        H                           1-21         H        H        OC.sub.2 H.sub.5                                                                        H        H                           1-22         H        H                                                                                       ##STR10##                                                                              H        H                           1-23         CH.sub.3 H        CH.sub.3  H        H                           1-24         OCH.sub.3                                                                              H        H         OCH.sub.3                                                                              H                           1-25         OCH.sub.3                                                                              OCH.sub.3                                                                              OCH.sub.3 H        H                           1-26         Cl       H        Cl        H        H                           1-27         H        Cl       Cl        H        H                           1-28         H        H        H         H        CH.sub.3                    1-29         H        H        H         H                                                                                       ##STR11##                  1-30         H        H        H         H                                                                                       ##STR12##                  1-31         H        H        Cl        H        CH.sub.3                    1-32         H        H        H         H        H                           __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________     ##STR13##                                                                    Compound No.       R.sub.8         R.sub.9                                    __________________________________________________________________________    1-33                                                                                              ##STR14##      H                                          1-34                                                                                              ##STR15##      H                                          1-35                                                                                              ##STR16##      H                                          1-36                                                                                              ##STR17##      H                                          1-37                                                                                              ##STR18##      H                                          1-38                                                                                              ##STR19##      H                                          1-39                                                                                              ##STR20##      H                                          1-40                                                                                              ##STR21##      H                                          1-41                                                                                              ##STR22##      H                                          1-42               C.sub.2 H.sub.5 H                                          1-43               CH.sub.3        CH.sub.3                                   1-44                                                                                              ##STR23##      H                                          1-45                                                                                              ##STR24##      H                                          __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________     ##STR25##                                                                    Compound No.                     X                                            __________________________________________________________________________    1-46                                                                                                            ##STR26##                                   1-47                                                                                                            ##STR27##                                   1-48                                                                                                            ##STR28##                                   1-49                                                                                                            ##STR29##                                   __________________________________________________________________________

These disazo compounds can be prepared easily according to themanufacturing process as mentioned above. That is, said disazo compoundcan be readily manufactured by diazotating the commercially available2,6-diaminothraquinone (produced by Aldrich Chemical Co., Milwaukee) ina normal manner to thereby obtain tetrazonium salt, and then subjectingthis salt and couplers corresponding thereto, 2-hydroxy-3-hydrazidenaphthoate and the like, to a coupling reaction in a proper solventsuch, for instance, as N-dimethylformamide (DMF) under the influence ofa base.

FIG. 1 is a grossly enlarged sectional view of an electrophotographicelement embodying the present invention. This element is designed toform, on an electrically conductive substrate 11, a photosensitive layer44 comprising a charge carrier generating layer 22 and a charge transferlayer 33.

As the electrically conductive layer suitably used in the presentinvention there can be enumerated metal plates, metal drums or metalfoil of aluminum, nickel, chromium and the like, plastic film providedwith thin layers of aluminum, tin oxide, indium oxide, chromium,palladium and the like, and electrically conductive substance-coated orimpregnated paper or plastic films.

The charge carrier generating layer is formed on the electricallyconductive substrate by coating the surface of the substrate with adispersion obtained by dispersing, in a suitable solvent, very finepowders of the above specified disazo compound having the generalformula (I) pulverized by means of a ball mill or the like and ifneeded, dissolving a binder resin thereto. The thus formed chargecarrier generating layer is surface-finished for instance by buffing orthe like and the film thickness if regulated as occasion demands.

The thickness of this charge carrier generating layer 22 is 0.01 to 5μm, preferably 0.05 to 2 μm. The percentage of disazo compound containedin the charge carrier generating layer is 10 to 100% by weight,preferably 30 to 95% by weight. In case the film thickness of the chargecarrier generating layer is less than 0.01 μm the sensitivitydeteriorates, and in case the film thickness is above 5 μm the potentialretainability deteriorates. Further, in case the percentage of disazocompound contained in the charge carrier generating layer is less than10% by weight the sensitivity deteriorates.

The charge transfer layer is formed by coating the surface of saidcharge carrier generating layer with a solution obtained by dissolvingvarious charge transfer substances and binder resins referred toafterwards in a proper solvent for instance such as tetrahydrofuran orthe like. The percentage of the charge transfer substance contained inthe charge transfer layer is 10 to 80% by weight, preferably 25 to 75%by weight, and the film thickness of said layer is 2 to 100 μm,preferably 5 to 40 μm. In case the percentage of the charge transfersubstance contained in the charge transfer layer is less than 10% byweight the sensitivity deteriorates, while in case said percentage isabove 80% by weight there are brought about undesirable results suchthat the film becames brittle and the charge transfer layer becomescloudy due to separated crystals. In case the thickness of the chargetransfer layer is less than 2 μm the potential retainabilitydeteriorates and in case said thickness is above 100 μm the residualpotential rises.

The typical examples of the charge transfer substance used in the chargetransfer layer will be shown below. ##STR30## (wherein, R¹⁰ stands foran alkyl group such as a methyl group, an ethyl group or the like; asubstituted alkyl group such as 2-chloroethyl group, 2-hydroxyethyl orthe like; R¹¹ stands for an alkyl group such as a methyl group, an ethylgroup or the like; an aralkyl group such as a benzyl group or the like;an aryl group such as a phenyl group or the like; R¹² stands forhydrogen; halogen such as chlorine, bromine or the like; an alkyl groupsuch as a methyl group, an ethyl group, a propyl group, a butyl group orthe like; an alkoxy group such as a methoxy group, an ethoxy group, apropoxy group, a butoxy group or the like; a dialkylamino group; or anitro group.) ##STR31## (wherein, Ar' stands for a naphthyl group, ananthryl group, a styryl group or substituents thereof; R¹³ stands for analkyl group such as a methyl group, an ethyl group or the like; anaralkyl group such as a benzyl group or the like; and an aryl group suchas a phenyl group. As the substituents on said naphthyl group, anthrylgroup and styryl group there can be enumerated, for instance, an alkylgroup such as a methyl group, an ethyl group or the like; an alkoxygroup such as a methoxy group, an ethoxy group or the like; adialkylamino group such as a dimethylamino group, a diethylamino groupor the like; and the like.) ##STR32## (wherein R¹⁴, R¹⁵ or R¹⁷ standsfor hydrogen; an alkyl group such as a methyl group, an ethyl group, apropyl group or the like; an alkoxy group such as a methoxy group, anethoxy group, a propoxy group or the like; halogen such as chlorine,bromine or the like; a nitro group; or a hydroxyl group; R¹⁶ stands forhydrogen, an alkyl group such as a methyl group, an ethyl group, apropyl group or the like; an alkoxy group such as a methoxy group, anethoxy group, propoxy group or the like; a dialkylamino group such as adimethylamino group, a diethylamino group or the like; a diaralkylaminogroup such as a dibenzylamino group or the like; a diarylamino groupsuch as a diphenylamino group or the like; halogen such as chlorine,bromine or the like; a nitro group or a hydroxyl group; and R¹⁸ standsfor an alkyl group such as a methyl group, an ethyl group or the like;an aralkyl group such as a benzyl group or the like; and an aryl groupsuch as a phenyl group or the like.) ##STR33## (wherein, R¹⁹, R²⁰, R²¹or R²² each stands for hydrogen; an alkyl group such as a methyl group,an ethyl group, a propyl group or the like; an alkoxy group such as amethoxy group, an ethoxy group, a propoxy group and the like; adialkylamino group such as a dimethylamino group, a diethylamino groupor the like; halogen such as chlorine, bromine or the like; a nitrogroup or a hydroxyl group.) ##STR34## (wherein, R²³ stands for an alkylgroup having carbon atoms of 1 to 11, a substituted or unsubstitutedphenyl group and a substituted or unsubstituted heterocyclic group; R²⁴or R²⁵ stands for hydrogen; an alkyl group such as methyl group, anethyl group, propyl group, a butyl group and the like; achloro-substituted alkyl group; a hydroxy-substituted alkyl group; and asubstituted or unsubstituted aralkyl group; and R²⁴ and R²⁵ may bondtogether to form a nitrogen-containing heterocycle. R²⁶ or R²⁷ standsfor hydrogen, an alkyl group such as methyl group, an ethyl group, apropyl group, a butyl group or the like; an alkoxy group such as amethoxy group, an ethoxy group or the like; and halogen such aschlorine, bromine or the like. The heterocyclic group in R²³ includes apyridyl group, a furyl group, a thienyl group, an indolyl group, apyrrolyl group, a quinolyl group, a carbazolyl group and the like. Asthe substituents on the phenyl group or the heterocyclic group in R²³include there can be enumerated an alkyl group such as a methyl group,an ethyl group or the like; an alkoxy group such as a methoxy group, anethoxy group, and the like. As the aralkyl group represented by R²⁴ orR²⁵ there can be enumerated for instance a benzyl group or the like, andas the substituents on the aralkyl group there can be enumerated halogensuch as chlorine, bromine or the like; an alkyl group such as a methylgroup, an ethyl group or the like; a nitro group and the like. Theheterocycle formed by bonding R²⁴ with R²⁵ includes a morpholine ring.##STR35## (wherein, R²⁸ stands for hydrogen; halogen such as chlorine,bromine or the like; R²⁹ stands for hydrogen; halogen such as chlorine,bromine or the like; an alkyl group such as a methyl group, an ethylgroup or the like; an alkoxy group such as methoxy group, an ethoxygroup or the like; a dialkylamino group such as a dimethylamino group, adiethylamino group, a dibutylamino group or the like; a diaralkylaminogroup such as a dibenzylamino group, a chloro-substituted dibenzylaminogroup or the like; a nitro group, a cyano group or ##STR36## and R³⁰stands for hydrogen; halogen such as chlorine, bromine or the like; andan alkyl group such as a methyl group, an ethyl group or the like.)##STR37## (wherein, R³¹ stands for hydrogen; halogen such as chlorinebromine or the like; an alkyl group such as a methyl group, an ethylgroup, a butyl group or the like; an alkoxy group such as a methoxygroup, an ethoxy group, an butoxy group, a cyano group or the like; R³²or R³³ stands for hydrogen; an alkyl group such as a methyl group, anethyl group, a butyl group or the like; a substituted alkyl group suchas 2-chloroethyl group, 2-hydroxyethyl group or the like or anunsubstituted benzyl group; and R³⁴ or R³⁵ stands for hydrogen; halogensuch as chlorine, bromine or the like; an alkyl group such as a methylgroup, an ethyl group, a butyl group or the like; an alkoxy group suchas a methoxy group, an ethoxy group, a butoxy group or the like; and adialkylamino group such as a dimethylamino group, a diethylamino groupor the like. As the substituents on the benzyl group in R³² or R³³ therecan be enumerated an alkyl group such as a methyl group, an ethyl groupor the like; an alkoxy group such as a methoxy group, an ethoxy or thelike; a nitro group or the like.) ##STR38## (wherein, Ar" stands forN-alkylcarbazolyl group. As the alkyl group there can be enumerated amethyl group, an ethyl group, a propyl group, a butyl group or thelike.) ##STR39## (wherein, R³⁶, R³⁷ and R³⁹ each stands for hydrogen;halogen such as chlorine, bromine or the like; an alkyl group such as amethyl group, an ethyl group or the like; an alkoxy group such as amethoxy group, an ethoxy group; a nitro group or an amino group. R³⁸stands for hydrogen; halogen such as chlorine, bromine or the like; analkyl group such as a methyl group, an ethyl group or the like; analkoxy group such as a methoxy group, an ethoxy group or the like; adialkylamino group such as a dimethylamino group, a diethylamino group,a dibutylamino group or the like; a substituted or unsubstituteddiaralkylamino group such as a dibenzylamino group, a chloro-substituteddibenzylamino group, a methyl-substituted dibenzylamino group, amethoxy-substituted dibenzylamino group or the like;N-alkyl-N-aralkylamino group such as N-methyl-N-benzylamino group or thelike; a carboxy group or its ester; an amino group; a hydroxy group; acyano group, or a acetylamino group.) ##STR40## (wherein, R⁴⁰ stands forN-alkylcarbazolyl group, a pyridyl group, a thienyl group, an indolylgroup, a furyl group or a substituted or unsubstituted naphthyl, styrylor anthryl group. As the substituents on the naphthyl group, the styrylgroup or the anthryl group there can be enumerated an alkyl group suchas a methyl group, an ethyl group or the group; an alkoxy group such asa methoxy group, an ethoxy group or the like; a dialkylamino group suchas a dimethylamino group a diethylamino group or the like.) ##STR41##(wherein R⁴¹ and R⁴² each stands for hydrogen; an alkyl group such as amethyl group, an ethyl group, a butyl group or the like; an alkoxy groupsuch as a methoxy group, an ethoxy group, a butoxy group or the like;halogen such as chlorine, bromine or the like; or a dialkylamino groupsuch as a dimethylamino group, a diethylamino group or the like. n₁ is 0or 1.) ##STR42## (wherein, R⁴³ and R⁴⁴ each stands for hydrogen; analkyl group such as a methyl group, an ethyl group or the like; analkoxy group such as a methoxy group, an ethoxy group or the like;halogen such as chlorine, R⁴⁵ and R⁴⁶ each stands for an alkyl groupsuch as a methyl group, an ethyl group, a propyl group, a butyl group orthe like; a substituted or unsubstituted aralkyl group, or a substitutedor unsubstituted aryl group, R⁴⁷ stands for hydrogen or a substituted orunsubstituted phenyl group. As the aralkyl group in R⁴⁵ and R⁴⁶ therecan be enumerated for instance a benzyl group, and as the aryl group inR⁴⁵ and R⁴⁶ there can be enumerated for instance a phenyl group. And,the substituents on the aralkyl group or the aryl group include an alkylgroup such as a methyl group, an ethyl group, a butyl group or the like;an alkoxy group such as a methoxy group, an ethoxy group or the like;halogen such as chlorine or the like; or a dialkylamino group such as adimethylamino group, a diethylamino group or the like.) ##STR43##(wherein, R⁴⁸ and R⁴⁹ each stands for an alkyl group such as a methylgroup, an ethyl group or the like; a substituted or unsubstituted phenylgroup, or a substituted or unsubstituted benzyl group. The substituentsthereon include an alkyl group such as a methyl group, an ethyl group orthe like and an alkoxy group such as a methoxy group, an ethoxy group orthe like.) ##STR44## (wherein, R⁵⁰ and R⁵¹ stand for the same groups asdefined above by R⁴⁸ and R⁴⁹.) ##STR45## [wherein, R⁵² stands forhydrogen, an alkyl group such as a methyl group, an ethyl group or thelike; or a substituted or unsubstituted phenyl group. n₂ is an integerof 0 or 1. A stands for ##STR46## 9-anthryl group or a substituted orunsubstituted N-alkylcarbazolyl group. Hereon, R⁵³ stands for hydrogen;an alkyl group; an alkoxy group, halogen, or a substituted amino grouprepresented by ##STR47## (R⁵⁴ and R⁵⁵ each may stand for an alkyl groupsuch as a methyl group, an ethyl group, a propyl group, a butyl group orthe like; a substituted or unsubstituted aralkyl group such as a benzylgroup or the like; a substituted or unsubstituted aryl group such as aphenyl group or the like, and R⁵⁴ and R⁵⁵ may bond to form a ring.). mis an integer of 0,1, 2 or 3. In case m is 2 or more, R⁵³ may be thesame group or different. As the substituents on the aralkyl group or thearyl group in R⁵⁴ or R⁵⁵ there may be enumerated an alkyl group such asa methyl group, an ethyl group, a propyl group, a butyl group or thelike; an alkoxy group such as a methoxy group, an ethoxy group or thelike; halogen such as chlorine; a dialkylamino group such as adiethylamino group or the like.]

Further, the concrete examples of these charge transfer substances areas shown in below.

    __________________________________________________________________________    Compound No.                                                                          structural formula                                                    __________________________________________________________________________    2-1                                                                                    ##STR48##                                                            2-2                                                                                    ##STR49##                                                            2-3                                                                                    ##STR50##                                                            2-4                                                                                    ##STR51##                                                            2-5                                                                                    ##STR52##                                                            2-6                                                                                    ##STR53##                                                            2-7                                                                                    ##STR54##                                                            2-8                                                                                    ##STR55##                                                            2-9                                                                                    ##STR56##                                                            2-10                                                                                   ##STR57##                                                            2-11                                                                                   ##STR58##                                                            2-12                                                                                   ##STR59##                                                            2-13                                                                                   ##STR60##                                                            2-14                                                                                   ##STR61##                                                            2-15                                                                                   ##STR62##                                                            2-16                                                                                   ##STR63##                                                            2-17                                                                                   ##STR64##                                                            2-18                                                                                   ##STR65##                                                            2-19                                                                                   ##STR66##                                                            2-20                                                                                   ##STR67##                                                            2-21                                                                                   ##STR68##                                                            2-22                                                                                   ##STR69##                                                            2-23                                                                                   ##STR70##                                                            2-24                                                                                   ##STR71##                                                            2-25                                                                                   ##STR72##                                                            2-26                                                                                   ##STR73##                                                            2-27                                                                                   ##STR74##                                                            2-28                                                                                   ##STR75##                                                            2-29                                                                                   ##STR76##                                                            2-30                                                                                   ##STR77##                                                            2-31                                                                                   ##STR78##                                                            2-32                                                                                   ##STR79##                                                            2-33                                                                                   ##STR80##                                                            2-34                                                                                   ##STR81##                                                            2-35                                                                                   ##STR82##                                                            2-36                                                                                   ##STR83##                                                            2-37                                                                                   ##STR84##                                                            2-38                                                                                   ##STR85##                                                            2-39                                                                                   ##STR86##                                                            2-40                                                                                   ##STR87##                                                            2-41                                                                                   ##STR88##                                                            2-42                                                                                   ##STR89##                                                            2-43                                                                                   ##STR90##                                                            2-44                                                                                   ##STR91##                                                            2-45                                                                                   ##STR92##                                                            2-46                                                                                   ##STR93##                                                            2-47                                                                                   ##STR94##                                                            2-48                                                                                   ##STR95##                                                            2-49                                                                                   ##STR96##                                                            2-50                                                                                   ##STR97##                                                            2-51                                                                                   ##STR98##                                                            2-52                                                                                   ##STR99##                                                            2-53                                                                                   ##STR100##                                                           2-54                                                                                   ##STR101##                                                           2-55                                                                                   ##STR102##                                                           2-56                                                                                   ##STR103##                                                           2-57                                                                                   ##STR104##                                                           2-58                                                                                   ##STR105##                                                           2-59                                                                                   ##STR106##                                                           2-60                                                                                   ##STR107##                                                           2-61                                                                                   ##STR108##                                                           __________________________________________________________________________

In addition to the above enumerated compounds, there can be effectivelyemployed any one of the following known charge transfer substancesincluding the high molecular substances such as poly-N-vinylcarbazole,halogenated-poly-N-vinylcarbazole, polyvinylpyrene or condensationresins such as bromopyreneformaldehyde condensation resin,N-ethylcarbazole-formaldehyde condensation resin and the like, and thelow molecular substances such as oxazole derivatives, oxadiazolederivatives, nitro derivatives of fluorenone and the like.

The binder resins used for the charge carrier generating layer hereininclude polyester resin, butyral resin, ethyl cellulose resin, epoxyresin, acryl resin, vinylidene chloride resin, polystyrene,polybutadiene and their copolymers. They may be used singly or in themixed state of two kinds or more.

The binder resins for use in the charge transfer layer includepolycarbonate resin, polyester resin, polystyrene, polyurethane resin,epoxy resin, acryl resin, silicone resin and their copolymers. They maybe used singly or in the mixed state of two kinds or more.

Further, various additives may be incorporated in the charge transferlayer for the purpose of improving its flexibility or durability. As theadditives used for this purpose there can be enumerated halogenatedparaffin, dialkyl phthalate, silicone oil and the like. In the case ofthe element according to the present invention, it is also possible toprovide a barrier layer between the electrically conductive substrateand the charge carrier generating layer, an intermediate layer betweenthe charge carrier generating layer and the charge transfer layer, andan overcoat layer on the charge transfer layer as occasion demands.

Still further, the disazo compounds having the general formula (I) ofthe present invention may be dispersed, taking the powdery form, in thebinder resin (which, if needed, may contain the charge transfersubstance). That is, said disazo compounds may also be used in adispersion type element.

The electrophotographic element of the present invention is constructedas mentioned above. Accordingly, as will be evident from examples andcomparative examples referred to afterwards, the electrophotographicelement of the present invention may be said to have superior propertiesthat it is produced easily as compared with the conventional multilayertype elements, it is high in sensitivity because its sensitive lightwavelengths are localized at the short wavelength region (about 450 to600 nm), and it is stable in characteristics even when used repeatedly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a grossly enlarged sectional view of an electrophotographicelement embodying the present invention.

FIG. 2 is a graph illustrating spectral sensitivity characteristics ofthe elements according to the present invention.

FIG. 3 is a graph illustrating spectral sensitivity characteristics ofthe comparative elements.

FIG. 4 is a view illustrating infrared absorption spectrums (KBr tabletmethod) of the typical disazo compounds according to the presentinvention.

PREFERRED EMBODIMENTS OF THE INVENTION

Next, the present invention will be explained substantially withreference to examples. However, it is to be understood that theembodiments of the present invention should not be limited thereto.

First, the preparation examples of the disazo compounds according to thepresent invention will be given as follows.

PREPARATION EXAMPLE

14.3 g (0.06 mol) of 2,6-diaminoanthraquinone (produced by AldrichChemical Co., Milwaukee) was mixed with 155 ml of 36% hydrochloric acidto obtain a mixture. A solution obtained by dissolving 9.0 g of sodiumnitrite in 30 ml of water was then dropped in said mixture at atemperature of -5° C. to 0° C. in about 20 minutes. After completion ofdropping, said solution was stirred for additional two hours at the sametemperature. Thereafter, it was poured in 3 l of cold water and wasfiltered to remove a small amount of insoluble matter. 40 ml of 42%borofluoric acid was added to this filtrate. Thus separated crystalswere filtered, were washed with about 50 ml of methanol and then driedto obtain 22.6 g (86.3%) ofanthraquinone-2,6-bisdiazoniumbistetrafluoroborate as light-browncrystals.

Infrared absorption spectrum (KBr disc)

νN₂ : 2310 cm⁻¹

νCO: 1695 cm⁻¹

Successively, 2.18 g, 0.005 mole, of the thus obtained tetrazonium saltand 0.01 mol of the coupler having the general formula (IV) weredissolved in 300 ml of DMF. Then, a solution dissolved 1.64 g of sodiumacetate in 14 ml of water was dropped thereinto at room temperature forabout 15 minutes. After completion of said dropping, it was stirred foradditional 2 hours, and then separated crystals were filtered out. Theresulting coarse crystal cake was dispersed in 300 ml of DMF was stirredat 80° C. for 2 hours. Thereafter, crystals were again filtered outtherefrom. This operation was repeated two times additionally. Then, thefiltered crystals were washed with water and dried, thereby obtainingthe disazo compound according to the present invention. The examples ofthe disazo compounds synthesized according to the above mentionedpreparation example will be shown Table 4 and Table 6.

These disazo compounds take the form of red or reddish purple powder atroom temperature. FIG. 4 indicates infrared absorption spectrums (KBrtablet method) of the typical disazo compounds expressed by Compound No.1-32 according to the present invention.

                                      TABLE 4                                     __________________________________________________________________________     ##STR109##                                                                                             Elementary analysis value                                                                  Melting                                                                            Infrared absorption               Compound                  (calculated point)                                                                         point                                                                              spectrum (KBr disc)               No.   R.sub.1                                                                            R.sub.2                                                                            R.sub.3                                                                            R.sub.4                                                                            C % H %  N % (°C.)                                                                       νNH (cm.sup.-1)                                                                   νco                     __________________________________________________________________________                                                       (cm.sup.-1)                1-32  H    H    H    H     71.27                                                                            4.01 13.26                                                                             >300 3210   1675                                                 (71.42)                                                                           (3.83)                                                                             (13.33)                                    1-1   OCH.sub.3                                                                          H    H    H    69.12                                                                             3.90 12.24                                                                             >300 3210   1675                                                 (69.32)                                                                           (4.03)                                                                             (12.44)                                    1-2   H    OCH.sub.3                                                                          H    H    69.16                                                                             3.93 12.46                                                                             >300 3200   1670                                                 (69.32)                                                                           (4.03)                                                                             (12.44)                                    1-3   H    H    OCH.sub.3                                                                          H    69.33                                                                             3.89 12.27                                                                             >300 3220   1675                                                 (69.32)                                                                           (4.03)                                                                             (12.44)                                    1-4   CH.sub.3                                                                           H    H    H    71.68                                                                             3.86 12.81                                                                             >320 3210   1675                                                 (71.87)                                                                           (4.18)                                                                             (12.90)                                    1-5   H    CH.sub.3                                                                           H    H    71.57                                                                             3.92 12.78                                                                             >300 3225   1675                                                 (71.87)                                                                           (4.18)                                                                             (12.90)                                    1-6   H    H    CH.sub.3                                                                           H    71.52                                                                             3.96 12.58                                                                             >300 --     1670                                                 (71.87)                                                                           (4.18)                                                                             (12.90)                                    1-10  Cl   H    H    H    65.98                                                                             3.31 12.12                                                                             >300 3200   1670                                                 (66.01)                                                                           (3.33)                                                                             (12.32)                                    1-11  H    Cl   H    H    65.87                                                                             3.05 11.99                                                                             >300 3225   1670                                                 (66.01)                                                                           (3.33)                                                                             (12.32)                                    1-12  H    H    Cl   H    65.93                                                                             3.16 12.03                                                                             >300 3210   1670                                                 (66.01)                                                                           (3.33)                                                                             (12.32)                                    1-18  NO.sub.2                                                                           H    H    H    64.33                                                                             3.02 14.94                                                                             >300 3190   1670                                                 (64.51)                                                                           (3.25)                                                                             (15.05)                                    1-19  H    NO.sub.2                                                                           H    H    64.29                                                                             3.02 14.80                                                                             >300 3200   1670                                                 (64.51)                                                                           (3.25)                                                                             (15.05)                                    1-20  H    H    NO.sub.2                                                                           H    64.33                                                                             3.05 14.80                                                                             >300 --     1675                                                 (64.51)                                                                           (3.25)                                                                             (15.05)                                    1-23  CH.sub.3                                                                           H    CH.sub.3                                                                           H    72.49                                                                             4.37 12.31                                                                             >300 3210   1670                                                 (72.31)                                                                           (4.50)                                                                             (12.49)                                    1-24  OCH.sub.3                                                                          H    H    OCH.sub.3                                                                          67.35                                                                             3.96 11.48                                                                             >300 3250   1680                                                 (67.49)                                                                           (4.20)                                                                             (11.66)                                    1-25  OCH.sub.3                                                                          OCH.sub.3                                                                          OCH.sub.3                                                                          H    65.52                                                                             4.19 10.67                                                                             >300 3200   1670                                                 (65.87)                                                                           (4.35)                                                                             (10.98)                                    1-21  H    H    OC.sub.2 H.sub.5                                                                   H    69.72                                                                             4.38 11.91                                                                             >300 3250   1675                                                 (69.82)                                                                           (4.34)                                                                             (12.06)                                    1-13  Br   H    H    H    59.65                                                                             2.89 10.99                                                                             >300 3200   1670                                                 (60.13)                                                                           (3.03)                                                                             (11.22)                                    1-14  H    Br   H    H    59.61                                                                             2.86 11.26                                                                             >300 3220   1670                                                 (60.13)                                                                           (3.03)                                                                             (11.22)                                    1-15  H    H    Br   H    60.16                                                                             2.96 10.91                                                                             >300 3200   1670                                                 (60.13)                                                                           (3.03)                                                                             (11.22)                                    __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________     ##STR110##                                                                                         Elementary analysis value                                                                  Melting                                                                            Infrared absorption                   Compound              (calculated point)                                                                         point                                                                              spectrum (KBr disc)                   No.   A               C % H %  N % (°C.)                                                                       νNH (cm.sup.-1)                                                                   νco (cm.sup.-1)             __________________________________________________________________________    1-37                                                                                 ##STR111##     73.95 (74.03)                                                                     3.53 (3.86)                                                                        11.70 (11.91)                                                                     >300 3200   1670                           1-44                                                                                 ##STR112##     73.88 (74.03)                                                                     3.71 (3.86)                                                                         11.69 (11.91)                                                                    >300 3220   1670                           1-41                                                                                 ##STR113##     72.01 (71.99)                                                                     3.89 (4.03)                                                                        11.00 (11.20)                                                                     >300 3220   1670                           1-38                                                                                 ##STR114##     75.99 (76.14)                                                                     3.72 (3.87)                                                                        10.80 (10.76)                                                                     >300 3200   1675                           1-45                                                                                 ##STR115##     77.06 (77.19)                                                                     3.68 (3.70)                                                                        10.55 (10.29)                                                                     >300 3220   1675                           1-35                                                                                 ##STR116##     64.80 (64.78)                                                                     3.12 (3.31)                                                                        13.35 (13.14)                                                                     >300 3200   1670                           1-39                                                                                 ##STR117##     73.55 (73.73)                                                                     4.22 (4.31)                                                                        12.95 (13.03)                                                                     >300 3200   1670                           __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________     ##STR118##                                                                                   Elementary analysis value                                                                  Melting                                                                            Infrared absorption                         Compound        (calculated point)                                                                         point                                                                              spectrum (KBr disc)                         No.   R.sub.5   % C H %  N % (°C.)                                                                       νNH (cm.sup.-1)                                                                   νco (cm.sup.-1)                   __________________________________________________________________________    1-28  CH.sub.3  71.67                                                                             4.01 12.77                                                                             >300 3240   1675                                 1-29                                                                                 ##STR119##                                                                             74.99 (75.28)                                                                     4.15 (4.34)                                                                        10.81 (10.98)                                                                     >300 3210   1675                                 1-30                                                                                 ##STR120##                                                                             74.83 (74.99)                                                                     3.78 (4.06)                                                                        11.10 (11.28)                                                                     >300 3170   1675                                 __________________________________________________________________________

EXAMPLE 1

76 parts by weight of disazo compound No. 1-32, 1260 parts by weight ofpolyester resin (VYLON 200: produced by TOYO BOSEKI K.K. (solidconcentration: 2%) and 3700 parts by weight of tetrahydrofuran werepulverized and mixed in a ball mill. The resulting dispersion wasapplied onto the aluminum face of an aluminum-vapordeposited polyesterbase (electrically conductive substrate) by means of doctor blade, andsame was air-dried to thereby form an about 1 μm-thick charge carriergenerating layer.

On the other hand, 2 parts by weight of charge transfer substance No.2-49, 2 parts by weight of polycarbonate resin (Panlite K 1300: producedby TEIJIN K.K.) and 16 parts by weight of tetrahydrofuran were mixed anddissolved to obtain a solution. Then, this solution was applied ontosaid charge carrier generating layer by means of a doctor blade, driedat 80° C. for 2 minutes and then dried at 100° C. for 5 minutes, therebyforming an about 20 μm-thick charge transfer layer. Thus, the multilayertype element No. 1 illustrated in FIG. 1 was prepared.

EXAMPLES 2 TO 33

The exactly same procedure as Example 1 except that the disazo compoundNo. 1-32 and charge transfer substance No. 2-49 employed in Example 1were replaced by the disazo compounds and charge transfer substancesshown in Table 7 referred to afterwards to thwereby prepare Elements No.2 to 33.

These Elements No. 1 to 33 were subjected to -6 KV corona discharge for20 seconds by means wof an electrostatic copying paper tester (SP 428TYPE: produced by Kawaguchi Electro Works) and charged negatively.Thereafter, these elements were left standing in the dark for 20 secondsto measure the surface potential Vpo(V) at that time. In succession,said elements were exposed to radiation of light from a tungsten lamp sothat the intensity of illumination on their surfaces may be 4.5 lux.And, the time (second) required until the surface potential was reducedto 1/2 of Vpo was found out and the exposure amount E1/2 (lux·sec) wascalculated therefrom on each element.

The thus obtained results are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Element                                                                              Disazo      Charge transfer                                                                           Vpo   E1/2                                     No.    Compound No.                                                                              substance No.                                                                             (volt)                                                                              (lux · sec)                     ______________________________________                                         1     1-32        2-49        -1289 9.1                                       2     1-32        2-44         -481 5.2                                       3     1-32        2-1         -1119 9.5                                       4     1-1         2-44        -1096 7.7                                       5     1-2         2-44         -291 4.8                                       6     1-2         2-1         -1065 6.5                                       7     1-2         2-49        -1303 7.1                                       8     1-4         2-44         -930 5.8                                       9     1-4         2-1         -1302 8.4                                      10     1-4         2-49        -1444 6.5                                      11     1-5         2-44         -406 4.8                                      12     1-5         2-1         -1083 5.9                                      13     1-5         2-49        -1439 5.3                                      14     1-6         2-44         -469 10.6                                     15     1-6         2-1         -1143 10.5                                     16     1-6         2-49        -1411 10.4                                     17     1-10        2-24        - 1543                                                                              10.3                                     18     1-10        2-44         -673 5.0                                      19     1-10        2-1         -1189 9.0                                      20     1-10        2-49        -1320 6.6                                      21     1-11        2-24        -1521 9.8                                      22     1-11        2-1         -1104 4.3                                      23     1-11        2-49        -1247 3.8                                      24     1-12        2-24        -1486 9.6                                      25     1-12        2-1          -879 5.6                                      26     1-12        2-49        -1315 4.5                                      27     1-18        2-44         -244 3.4                                      28     1-18        2-1         -1243 7.3                                      29     1-18        2-49        -1061 8.1                                      30     1-19        2-1          -857 3.9                                      31     1-19        2-49        -1063 4.2                                      32     1-20        2-1          -420 5.1                                      33     1-20        2-49         -703 11.0                                     ______________________________________                                    

COMPARATIVE EXAMPLE 1

The multilayer type element disclosed in U.S. Pat. No. 3,871,882,wherein a perylene derivative is incorporated in the charge carriergenerating layer and an oxadiazole derivative is incorporated in thecharge transfer layer, was prepared in the undermentioned manner.

N,N'-dimethylperylene-3,4,9,10-tetracarboxylic acid diimide was used asthe charge carrier generating substance, and same was vacuumvapordeposited on an aluminum plate under the conditions: degree ofvacuum 10⁻⁵ mmHg, vapordeposition source temperature 300° C. andvapordeposition time 3 minutes to thereby form the charge carriergenerating layer. In succession, a solution comprising 5 parts by weightof 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 5 parts by weight ofpolyester resin (Polyester Adhesive 49,000, produced by Du Pont Co.) and90 parts by weight of tetrahydrofuran was applied on the resultingcharge carrier generating layer, and dried at 120° C. for 10 minutes tothereby form the charge transfer layer having a thickness of about 10μm. Thus, Comparative element No. 1 was prepared.

COMPARATIVE EXAMPLE 2

The multilayer type element disclosed in Japanese Patent Publication No.42380/1980, wherein Chloro Dian Blue was incorporated in the chargecarrier generating layer and a hydrazon compound was incorporated in thecharge transfer layer, was prepared in the undermentioned manner.

A solution comprising 25 parts by weight of Chloro Dian Blue, 1240 partsby weight of ethylene diamine, 990 parts by weight of n-butylamine and2740 parts by weight of tetrahydrofuran was applied on the aluminum faceof an aluminum-vapordeposited polyester base with a 25μ wet gap by meansof a doctor blade and dried to thereby form the charge carriergenerating layer. In succession, a solution comprising 10 parts byweight of 4-diethylaminobenzaldehyde 1,1-diphenylhydrazone, 10 parts byweight of polycarbonate resin (the same as the resin employed inExample 1) and 80 parts by weight of tetrahydrofuran was applied on thethus formed charge carrier generating layer by means of a doctor bladeand dried to thereby form the charge transfer layer having a thicknessof about 18μ. Thus, Comparative element No. 2 was prepared.

COMPARATIVE EXAMPLE 3

The multilayer type element disclosed in Japanese Laid Open PatentApplication No. 84943/1980, wherein a distyrylbenzene type disazocompound was incorporated in the charge carrier generating layer and ahydrazone compound was incorporated in the charge transfer layer, wasprepared in the undermentioned manner.

20 parts by weight of4',4"-bis[2-hydroxy-3-(2,4-dimethylphenylcarbamoyl)-1-naphthylazo]-1,4-distyrylbenzene,3 parts by weight of polyvinylbutyral (Denka Butyral #4000-1, producedby Tokyo Denki Kagaku K.K.), 7 parts by weight of polymethylmethacrylate (DIANAL BR-80, produced by Mitsubishi Rayon K.K.) and 300parts by weight of tetrahydrofuran were ball-milled for 3 hours tothereby obtain a dispersion. This dispersion was diluted with 2700 partsby weight of tetrahydrofuran. Thereafter, this dispersion was applied onthe aluminum face of an aluminum-vapordeposited polyester base(electrically conductive substrate) by means of a doctor blade and driedto thereby form an about 0.3 μ-thick charge carrier generating layer. Insuccession, a solution comprising 10 parts by weight of1-methyl-1-phenyl hydrazone, 10 parts by weight of polycarbonate resin(the same resin as employed in Example 1) and 80 parts by weight oftetrahydrofuran was applied on said charge carrier generating layer anddried to thereby form an about 13 μ-thick charge transfer layer. Thus,Comparative multilayer type element No. 3 was prepared.

For the purpose of measuring the sensitive wavelengths for thesecomparative elements No. 1 to 3 and the elements No. 23 and 31 of thepresent invention, said elements were subjected to spectral sensitivitymeasurement in accordance with the following procedure.

First, each element was charged by corona discharge in the dark so thatits surface potential may become more than -800 V, and then subjected todark decay until the surface potential becomes -800 V. When the surfacepotential became -800 V, the element was exposed to a monochromaticspectrum obtained by means of a monochrometer, its intensity ofillumination on the element being 1 μW/cm². And, the time required untilthe surface potential decayed to -400 V was found out, and the halfdecay exposure amount (μW·sec/cm²) was calculated therefrom. On theother hand, the potential difference to be obtained actually by theexposure was found out by substracting the dark decayed potentialportion from the apparent potential difference 400 V to be obtained bythe exposure. Then, the light decay speed (Volt·cm² ·μW⁻¹ ·sec⁻¹) wascalculated from the actual potential difference and half decay exposureamount and named sensitivity. The thus obtained results were shown inFIGS. 2 and 3.

- ○ - ○ - Element No. 10 (FIG. 2)

- - - Element No. 19 (FIG. 2)

-x-x- Comparative Element No. 1 (FIG. 3)

- - - Comparative Element No. 2 (FIG. 3)

- - - Comparative Element No. 3 (FIG. 3)

COMPARATIVE EXAMPLES 4 AND 5

For comparisons' sake, Comparative elements No. 4 and No. 5 wereprepared respectively by repeating the exactly same procedure asemployed in the preparation of the above element of the presentinvention described in Example 1 except that the charge transfersubstance No. 2-49 replaced by substance No. 2-1 and the disazo compoundof the present invention was replaced by (1)4,4'-bis(2-hydroxy-3-phenylcarbamoyl-1-naphthylazo)-3,3'-dichlorodiphenyl(Chloro Dian Blue) coming under the benzidine type disazo compoundsdisclosed in the above mentioned Japanese Laid Open Patent ApplicationsNos. 37543/1970 and 55643/1977, and (2)4,4'-bis(2-hydroxy-3-phenylcarbamoyl-1-naphthylazo)stilbene coming underthe stilbene type disazo compounds disclosed in Japanese Laid OpenPatent Application No. 8832/1977, respectively.

The thus prepared comparative elements No. 4 and No. 5 together with theelement No. 30 according to the present invention were subjected toelectrostatic characteristic measurement by means of a commerciallyavailable electrostatic copying paper tester (SP-428 TYPE, produced byKawaguchi Electro Works). In more detail, said elements were firstsubjected to -6 KV corona discharge for 20 seconds and chargednegatively to thereby measure the surface potential at that time andfind out Vdo (V). Then, the said elements were left standing in the darkfor 20 seconds for dark decay purpose to thereby measure the surfacepotential at that time the find out Vdo (V). In succession, the elementswere exposed to radiation of light from a tungsten lamp so that theintensity of illumination on their surfaces may be 4.5 lux. And, thetime required until the surface potential was reduced to 1/2 of Vpo wasfound out and named the exposure amount E1/2(lux·sec). Likewise, thetime required until the surface potential Vpo was reduced to 1/5 and1/10 were found out respectively, and then the exposure amount E1/5(lux·sec) and the surface amount E1/10(lux·sec) were calculatedtherefrom respectively. The obtained results were shown in Table 8.

                                      TABLE 8                                     __________________________________________________________________________            Vdo Vpo Vpo/                                                                              E 1/2 E 1/5 E 1/10                                        Element (V) (V) Vdo (lux · sec)                                                                (lux · sec)                                                                (lux · sec)                          __________________________________________________________________________    Our     -1230                                                                              -857                                                                             .697                                                                              3.9    7.3   9.1                                          element No. 30                                                                Comparative                                                                            -940                                                                              -693                                                                             .738                                                                              5.9   12.3  16.7                                          element No. 4                                                                 Comparative                                                                           -1817                                                                             -1501                                                                             .826                                                                              19.3  51.0  75.0                                          element No. 5                                                                 __________________________________________________________________________

It can be seen from the above results that the element using the disazocompound according to the present invention is high in sensitivity andits sensitive wavelengths cover the range of about 460 to 600 nm.Accordingly, the element according to the present invention is superiorin the reproductivity of red image and so can dispense with a red filterwhen actually set in a copying machine.

Further, as the preparation of the electrophotographic element accordingto the present can dispense with the necessity of employing the vacuumvapordeposition as used in the preparation of said comparative elementNo. 1 or using the organic amine as used in the preparation of saidcomparative element No. 2, the element of the present invention shouldbe said profitable from the viewpoint of production.

Still further, the elements Nos. 23 and 31 of the present invention wereeach subjected to 10,000 times repeated reproduction by means of acopying machine RICOPY P-500 manufactured by RICOH COMPANY, LTD. As theresult, each element was found to produce a clear-out image. It may beunderstood therefrom that the elements of the present invention areextremely superior in durability.

What is claimed is:
 1. A disazo compound having the formula ##STR121##wherein R₁ and R₂ are the same or different and each stands forhydrogen; alkyl having 1 to 4 carbon atoms; a first radical selectedfrom the first group consisting of benzyl, phenetyl, phenyl, naphthyl,anthryl, pyrenyl, anthraquinonyl, thienyl, furyl, pyridyl andcarbazolyl; a second substituted radical in which said first radical issubstituted with alkyl having 1 to 4 carbon atoms, alkoxy having 1 to 4carbon atoms, halogen, cyano, nitro or dialkylamino having from 2 to 8carbon atoms; or R₁ and R₂ together with the carbon atom to which theyare attached form a first ring selected from the second group consistingof hexylidene, pentylidene, benzopentylidene and dibenzopentylidene, ora second substituted ring in which said first ring is substituted withalkyl having 1 to 4 carbon atoms, alkoxy having 1 to 4 carbon atoms,halogen, cyano, nitro or dialkylamino having from 2 to 8 carbon atoms.2. A disazo compound according to claim 1, wherein R₁ and R₂ each standsfor hydrogen, methyl, ethyl, propyl, said first radical or said secondsubstituted radical.
 3. A disazo compound according to claim 1 in whichR₁ is hydrogen and R₂ is phenyl or phenyl substituted with at least onesubstituent selected from the group consisting of alkyl having 1 to 4carbon atoms, alkoxy having 1 to 4 carbon atoms, halogen, cyano, nitroor dialkylamino having 2 to 8 carbon atoms.
 4. A disazo compoundaccording to claim 1, wherein R₁ and R₂ together with the carbon atom towhich they are attached form said first ring or said second substitutedring.
 5. A disazo compound according to claim 1, wherein R₁ is hydrogenand R₂ is a third radical selected from the third group consisting ofphenyl, naphthyl, anthryl, pyrenyl, thienyl and carbazolyl, and a fourthsubstituted radical in which said third radical is substituted withalkyl having 1 to 4 carbon atoms, alkoxy having 1 to 4 carbon atoms,halogen, cyano, nitro or dialkylamino having 2 to 8 carbon atoms.
 6. Adisazo compound according to claim 1, wherein R₁ is hydrogen and R₂ isphenyl, phenyl substituted with C₁ -C₄ lower alkyl-, C₁ -C₄ loweralkoxy-, halogen- or nitro, naphthyl, anthryl, pyrenyl, thienyl orcarbazolyl.
 7. A disazo compound according to claim 1, wherein R₁ ishydrogen and R₂ is phenyl, o-, m- or p-methoxyphenyl, o-, m- or p-methylphenyl o-, m- or p-chlorophenyl or o-, m- or p-nitrophenyl.
 8. A disazocompound according to claim 1, wherein R₁ is hydrogen and R₂ is o-, m-or p-bromophenyl, 2,4-dimethylphenyl, 2,5-dimethoxyphenyl,2,3,4-trimethoxyphenyl or 4-ethoxyphenyl.
 9. A disazo compound accordingto claim 1, wherein R₁ is hydrogen and R₂ is ##STR122##
 10. A disazocompound according to claim 1, wherein R₁ is phenyl and R₂ is methyl,phenyl or benzyl.